Ryan McLemore

Corticosterone modulation of reproductive and immune systems trade-offs in female tree lizards: long-term corticosterone manipulations via injectable gelling material.

SUMMARY Physiological trade-offs arise because multiple processes compete for the same limiting resources. While competition for resources has been demonstrated between reproduction and immune function, the regulation of this competition remains unclear. Corticosterone (CORT) is a likely mediator due to its dual role in mobilizing energy stores throughout the body and regulating physiological responses to stressors. We manipulated CORT concentrations and resources in pre-reproductive and reproductive female tree lizards (Urosaurus ornatus) to test the hypothesis that CORT regulates the distribution of limiting resources between the reproductive and immune systems. To manipulate circulating concentrations of CORT we utilized a novel method of hormone implantation, in which a polymeric compound is mixed with hormone and injected in liquid form into the animal. After injection, the liquid quickly gels in situ forming a slow release hormone implant. This method of hormone delivery eliminated the need for substantial wounds to the animal or repeated handling required by other methods. In this study, the hormone-treated animals had plasma CORT concentrations comparable to high physiological concentrations. We found that CORT treatment suppressed immune function, but only when animals were energetically compromised. We assessed immune function by measuring the healing rate of a cutaneous biopsy. Healing was suppressed in all CORT-treated reproductive animals and in all CORT-treated animals (pre-reproductive and reproductive) undergoing food restriction, but CORT had no effect in ad libitum non-reproductive females. The context-dependent action of CORT renders its response adjustable to changing environmental conditions and may allow for the suppression of specific functions depending on resource availability.

Particle size of fillers affects permeability of polymethylmethacrylate.

Particulate soluble filler added to polymethylmethacrylate increases its permeability, leading to increased elution. We asked whether particle size affects permeability and elution rate associated with a given volume fraction of filler. Permeability of filler-loaded PMMA was measured in 9 mm rods with a 32% volume fraction of four particle sizes (106 μm, 212 μm, 425 μm, 850 μm) and two filler materials (sucrose and xylitol) using a modified phenolphthalein-sodium hydroxide technique, which allowed quantitative serial observation on the same specimens. Fluid penetration was faster for larger particle sizes. The elution rate was greater for smaller particle sizes on qualitative visual assessment. Sucrose fillers were not different from xylitol fillers independent of particle size. For the volume fraction of 32%, larger particles lead to larger caliber porosity, less pore intercon nectivity, and faster fluid penetration. Smaller size particles lead to smaller caliber porosity, greater pore interconnectivity, smaller areas between the pores with no fluid penetration and greater increase in the effective surface area causing a greater elution rate.

Transforaminal lumbar interbody fusion with rhBMP-2 in spinal deformity, spondylolisthesis, and degenerative disease--part 2: BMP dosage-related complications and long-term outcomes in 509 patients.

Study Design. Retrospective review of prospectively collected data. Objective. Without industry funding, the study evaluated short- and long-term complications related to off-label bone morphogenetic protein (BMP) used with transforaminal lumbar interbody fusion (TLIF) from a large consecutive series. Complications and results were analyzed by BMP dose, fusion length, and primary versus revision surgery. Based on the results, surgical technique and BMP dose recommendations were proposed. Summary of Background Data. Off-label use of BMP in TLIF, although common, has only been studied in small series and case reports using various techniques, cage types, and doses of BMP. Several of these studies have reported minimal complications. Others report problems related to BMP, which has led to questions regarding current widespread use of TLIF with BMP. Method. TLIF with rhBMP-2 was performed at 872 discs in 509 consecutive adults who underwent open posterior instrumented fusion and had minimum 2-year follow-up; diagnoses included degenerative disease (179), spondylolisthesis (207), deformity (123). Patient age averaged 61 years: 12% were smokers and 41% had revision surgery. TLIF was performed at 1.7 levels: single level: 229, 2 levels: 201, 3 levels: 74, 4 levels: 5. Local autograft was used for backfill around and behind each rectangular cage. Varying doses of interbody BMP were used at an average 7.3 mg per disc (range: 2–12 mg per disc). Results. At 5 years average follow-up, 8 patients developed pseudoarthrosis at levels of TLIF (8 of 872 discs, 0.92%). Seroma (0.4%) and ectopic bone growth (0.6%) were too infrequent to be associated with a particular BMP dose. Deep infection was 2.6% overall (1.7% of the degenerative group). Symptomatic osteolysis or cage subsidence did not occur. Significant long-term improvement was noted in clinical and functional outcomes compared with preoperation. Conclusion. Five-year follow-up after TLIF with BMP, independent of industry, confirms effective arthrodesis in short and long fusions, both primary and revision. Most complications occurred in deformity patients. BMP-related complications (seroma, ectopic bone) were rare. Level of Evidence: 3

Amphotericin B Delivery From Bone Cement Increases With Porosity but Strength Decreases

BackgroundAmphotericin B is a highly hydrophobic antifungal used for orthopaedic infections. There is disagreement about whether amphotericin B is released when it is loaded in polymethylmethacrylate (PMMA). It is unknown how much a poragen will increase amphotericin B release or decrease the compressive strength of the PMMA.Questions/purposesWe therefore measured amphotericin B release and the compressive strength of amphotericin B loaded bone cement with and without adding high-dose poragen.MethodsAntifungal-loaded bone cement was formulated with Simplex P cement and 200 mg amphotericin B with and without 10 g cefazolin (poragen) per batch. Twenty standardized test cylinders were eluted in deionized water for each formulation. Cumulative amphotericin B mass and compressive strength were measured. Data were analyzed using repeated-measures analysis of variance.ResultsAntifungal-loaded bone cement (ALBC) with 10 g poragen delivered more amphotericin B than ALBC containing amphotericin B alone by Day 15, 12.76 μg/cylinder (0.5%) versus 1.74 μg/cylinder (0.04%), respectively. With amphotericin B alone, compressive strength was unchanged and compressive strength did not decrease during elution. Adding 10 g poragen to ALBC with 200 mg amphotericin B decreased the compressive strength and compressive strength decreased further during elution, 80, 61, and 46 MPa at 0, 1, and 30 days, respectively.ConclusionsAmphotericin B is released in very small amounts from antifungal-loaded bone cement. Release can be increased by adding high-dose poragen, but compressive strength decreases sufficiently to limit its use for implant fixation.

Transforaminal lumbar interbody fusion with rhBMP-2 in spinal deformity, spondylolisthesis, and degenerative disease--part 1: Large series diagnosis related outcomes and complications with 2- to 9-year follow-up.

Study Design. Retrospective review of prospectively collected data. Objective. To evaluate long-term clinical outcomes and complications of the transforaminal lumbar interbody fusion (TLIF) procedure from a large consecutive series, without industry funding. Clinical outcomes and complications are analyzed by diagnosis and primary versus revision surgery to assess whether TLIF with bone morphogenic protein (BMP) is appropriate for common use in deformity, spondylolisthesis, and degenerative disease. Summary of Background Data. A common method for achieving spinal arthrodesis includes TLIF with a cage and off-label interbody BMP-2, supported by posterior arthrodesis and a pedicle screw construct. There are no large studies analyzing outcomes and complications after TLIF in different diagnoses, for primary and revision surgery, leading some to question the widespread use of TLIF. Methods. A total of 509 consecutive adults underwent open posterior instrumented fusion, augmented with TLIF at 872 discs using a cage and rhBMP-2, with minimum 2-year follow-up. Cohort diagnoses included 179 degenerative, 207 spondylolisthesis, and 123 deformity patients. Patient age averaged 61 years, 207 had undergone prior decompression or fusion surgery. All patients underwent posterior instrumented fusion and pedicle screw instrumentation at average 3.6 levels (range, 1–16); all patients had TLIF 1.7 levels (range, 1–4 levels) with BMP and autograft, stabilized with an interbody cage. Results. At average 59 months follow-up, 12 patients developed pseudoarthrosis, 8 at TLIF levels (8/872 discs, 0.92%) most commonly at L5–S1 (6/8). Significant clinical improvement was noted in patients with deformity, spondylolisthesis, and degenerative disease undergoing primary and revision surgery. Overall, visual analogue scale preoperative score was 6.6, at 1 year 3.8, at 2 years 3.5 (P < 0.001) and the preoperative ODI was 50.9, at 1 year 36.1, and at 2 years 35.0 (P < 0 0.001). Pain medication requirements also declined. Conclusion. The efficacy of TLIF with BMP is supported in this large series with long-term follow-up, independent of industry. Reliable fusion and improved outcomes can be expected in adults undergoing TLIF for deformity, spondylolisthesis, and degenerative disease. Most complications occurred in patients with deformity. Level of Evidence: 3

Liposomal Formulation Increases Local Delivery of Amphotericin from Bone Cement: A Pilot Study

BackgroundAmphotericin is a highly toxic hydrophobic antifungal. Delivery of amphotericin from antifungal-loaded bone cement (ALBC) is much lower than would be expected for an equivalent load of water-soluble antibacterials. Lipid formulations have been developed to decrease amphotericin toxicity. It is unknown how lipid formulations affect amphotericin release and compressive strength of amphotericin ALBC.Questions/purposesWe asked if amphotericin release from liposomal amphotericin ALBC (1) changed with amphotericin load; (2) differed from release from amphotericin deoxycholate ALBC; (3) was an active drug; and (4) if liposomal amphotericin affected the bone cement strength.MethodsForty-five standardized test cylinders were fabricated from three formulations of ALBC: Simplex™ P bone cement with 200 mg liposomal amphotericin, 800 mg liposomal amphotericin, or 800 mg amphotericin deoxycholate per batch. For each ALBC formulation, cumulative released amphotericin was determined from five cylinders, and compressive strength was measured for 10 cylinders, five before elution and five after. Activity of released amphotericin was determined by growth inhibition assay.ResultsAmphotericin release was greater for increased load of liposomal amphotericin: 770 μg for 800 mg versus 118 μg for 200 mg. Amphotericin release was greater from liposomal ALBC than from deoxycholate ALBC: 770 μg versus 23 μg over 7 days for 800 mg amphotericin. Released amphotericin was active. Compressive strength of liposomal ALBC is decreased, 67 MPa and 34 MPa by Day 7 in elution for the 200-mg and 800-mg formulations, respectively.ConclusionsLiposomal amphotericin has greater amphotericin release from ALBC than amphotericin deoxycholate. Compressive strength of liposomal amphotericin ALBC decreases to less than recommended for implant fixation. Local toxicity data are needed before liposomal amphotericin ALBC can be used clinically.

Clavicular Length: The Assumption of Symmetry

Recent studies have shown subjectively worse outcomes associated with 15 to 20 mm of clavicle shortening. As a result, more than 15 mm of shortening has become a relative indication for operative management. Various methods to quantify shortening have been described in the literature. All measurement techniques described assume clavicular symmetry to assess clavicular shortening. The goal of this study was to assess the side-to-side variation in clavicle length in uninjured, skeletally mature adults.Clavicle length in 102 skeletally mature adults (age range, 22-91 years) was measured using computed tomography data. Clavicle length was defined as the distance between the lateral-most point of the clavicle in the acromioclavicular joint and the medial-most point of the clavicle in the sternoclavicular joint. The side-to-side difference in clavicular length was analyzed, and patients were organized into 2 groups: group 1 was symmetric (difference of less than 5 mm), and group 2 was asymmetric (difference of more than 5 mm). Mean difference in clavicle length for all patients was 4.25±3.8 mm (range, 0-23 mm). Clavicular symmetry was found in 73 (71.5%) of 102 patients. The remaining 29 patients had asymmetry greater than 5 mm. Asymmetry greater than 10 mm was found in 7 (7%) of 102 patients. Twenty-eight percent of clavicles were asymmetric, whereas 7% had clinically significant asymmetry that could affect treatment decisions.This finding calls into question previous methods developed to assess clavicular length in the setting of trauma because of the assumption of symmetry. Further studies are needed to evaluate the effect of hand dominance and pediatric trauma on this observation.

Effect of Body Mass Index on Limb Alignment After Total Knee Arthroplasty

Prior studies have reported increased failure rates in obese patients with postoperative limb mal-alignment. This study was undertaken to determine if a relationship exists between postoperative limb alignment and BMI in patients undergoing primary TKA performed with mechanical instruments. An IRB-approved retrospective review of 196 knees was undertaken. Limb alignment was determined on full-length, standing, hip-to-ankle x-rays, preoperatively and postoperatively. The effects of gender, side, preoperative mechanical alignment and BMI on postoperative alignment were analyzed via multivariate regression analysis. Both preoperative mechanical limb alignment (P<0.001) and BMI (P=0.009) had a significant effect on postoperative limb alignment following TKA performed with mechanical instruments.

In vivo evaluation of injectable thermosensitive polymer with time-dependent LCST

The focus of this study was to examine the biocompatibility, time-dependent LCST, and bioerodable properties of a copolymer system composed of NIPAAm, dimethyl-gamma-butyrolactone (DMBL), and acrylic acid (AAc). Sprague Dawley rats were subcutaneously injected with 25 wt % solutions of poly(NIPAAm-co-DMBL-co-AAc). At predetermined times, animals were sacrificed and polymer implants were recovered for characterization via 1H-NMR. In addition, polymer-contacting tissue sections were harvested and processed for histology. The biocompatibility of the implants was assessed by counting the number of fibroblasts and leukocytes present at the tissue-implant interface. The LCST data obtained from the in vivo implants was shown to agree with that of in vitro findings. Implant mass was shown to decrease after 4 days, indicating accelerated diffusion rates with increased implant swelling, hydrolytic degradation was confirmed with 1H-NMR measurements. The cellular presence at the copolymer implant-tissue interface was shown to return to that of normal tissue 30 days postimplantation, which suggests a normal wound healing response.

In situ forming, resorbable graft copolymer hydrogels providing controlled drug release.

In situ forming hydrogels are promising drug delivery vehicles due to their ease of delivery as liquids and their ability to be used in sites with irregular geometries. In this work, we report on in situ forming, resorbable hydrogels based on N-isopropylacrylamide (NIPAAm) as a fluid-like controlled release gel. These gels are the first resorbable NIPAAm-based gels providing controlled release without relying on affinity between the drug and device. Therefore, these gels provide a more flexible delivery system which can be used to deliver any drug at a controlled rate. The polymers contain repeat units of NIPAAm with (R)-α-Acryloyloxy-β,β-dimethyl-γ-butyrolactone (DBLA) and varying amounts of hydrophilic Jeffamine® M-1000 acrylamide (JAAm) grafts. The graft copolymer architecture allows the water content of the hydrogels to be tuned over a wide range while keeping the initial gelation temperature below body temperature. Incorporation of JAAm in the polymers led to greater water content, faster gel degradation, and reduced burst release. Sustained release of the antimicrobial drugs cefazolin and vancomycin (over about 5 and 7 days, respectively) was observed from gels containing an intermediate amount of grafts which combined reduced phase separation with a degradation time of 40 days. The degradation byproducts of one hydrogel formulation were cytocompatible to NIH 3T3 fibroblasts at concentrations up to 2.5 wt %. This class of terpolymer hydrogels is a promising local delivery system for a wide variety of drugs, particularly for applications involving irregular geometries such as implant interfaces.